Seven years ago, Barbuto faced charges for misappropriating $80,000 from the Cape Cod golf course he managed and squandering more than half the money on Oxycontin. Walsh, 13 years his senior and a coach from his Little League days, stepped in to help, reassuring Barbuto’s parents, getting him treatment, taking him to Alcoholics Anonymous meetings, vouching for him with the court. Walsh was by then a state legislator, a recovering alcoholic who knew a thing or two about addiction. Barbuto thought of him only as a friend.

Now, Walsh is a finalist to become Boston’s next mayor, and Barbuto is among the volunteers who make up the most unorthodox and perhaps most ardent group of volunteers of this campaign season: reformed alcoholics and drug addicts whose shared vulnerability has made them devoted acolytes of Walsh. A constituency that is seldom politically acknowledged and never politically organized, these volunteers are approaching the campaign with uncommon emotional investment. After all, they have been given a new lease on life, and some of them credit their second chance directly to Walsh.

“I love this guy so much. And there are so many guys like me on the campaign,” said Stephen Passacantilli, who met Walsh when he was newly sober and who is now a regional field director for his campaign. “I will run through a wall for him, if that meant he’s going to be the mayor of Boston.”

To the recovery community in Boston, Walsh is not just a shining success story but also a personal patron. A Savin Hill kid whose life spiraled out of control in his 20s, he quit drinking 18 years ago and began helping others do the same. In the Legislature, he became the leading advocate for funding for substance abuse treatment programs.

‘His experience being in recovery is a window into all these other worlds where he’s able to empathize in a way that I don’t think other people can.’

Brendan Little

He’s also a go-to guy who fields calls on his cellphone, even while he’s on the campaign trail, from people who desperately need help finding beds in detox centers or group meetings close to home.

Passacantilli, 38, who worked as Walsh’s driver during the preliminary campaign, heard the calls coming in, sometimes several times a day. “Even when I’m in the truck with him, he will stop what he’s doing when he gets one of those phone calls,” he said. “God forbid you don’t answer that phone.”

Now, Walsh is being repaid for that service with hours of door-knocking, phone-calling, and testimonials from those who have been on the receiving end of it — or who have seen that kind of crisis in their families and admire Walsh’s willingness to help.

His previously quiet role in the recovery community has been somewhat tricky to navigate as a candidate for mayor, he acknowledges — and not because of the political sensitivities that one might expect.

People may not vote for him because he’s an alcoholic, he acknowledges. That’s fine, he says; other voters have lived through it in their families and get it. “I don’t really care who knows I’m an alcoholic because if it helps somebody else knowing that I’m an alcoholic, then they’ll ask me for help if they need it,” Walsh said in an interview.

Instead, he said, he grappled with how “people in the program” would react to his personal story becoming public during his campaign. Alcoholics Anonymous is adamant about steering clear of politics. As a group, it won’t endorse or oppose anyone or anything that might distract members from their one shared mission — to stay sober and help other alcoholics to do so.

“We’re not organizing in the halls of AA,” Walsh said. “That’s not appropriate.”

Still, word got around, and individual volunteers enlisted.

“It’s been funny since I’ve joined up, I’ve run into other recovery people that I’ve known along the way and they’re sort of united around Marty,” said Brendan Little, a 27-year-old musician who left home at 13 and was living on the street, drinking and doing drugs. He didn’t meet Walsh until just before the campaign, but there, he found common ground with other staffers and volunteers.

“It sort of feels like this pull to people. I feel like I could be in a room with 10 people and I’ll know who the alcoholic is, even if they’re 20 years sober. There’s just a sense,” Little said. “I’ll make friends with somebody and then find out they’re in recovery. Of course. We’ll find each other.”

Little, who serves as the Walsh campaign’s policy coordinator, thinks that his candidate’s own hard-earned lessons help him identify with a wide range of people, even those “compelled to do something that’s harmful,” such as prostitution.

“His experience being in recovery is a window into all these other worlds where he’s able to empathize in a way that I don’t think other people can,” Little said.

Though Walsh doesn’t use his sobriety in his stump speech, it comes up on the trail. At his campaign kickoff, he was introduced by James Taylor, a 61-year-old Dorchester resident Walsh had helped years ago, on a night Walsh was at Boston Medical Center to help someone else get into detox. Taylor was down and out, with no place to go. Walsh got him into a halfway house and invited him to come visit the State House after he got his act together.

“I’ve asked myself, ‘if that had been me, would I have helped that person?’ ” said Taylor. “Probably not.”

So, on many days, Taylor has been out knocking on voters’ doors, singing Walsh’s praises to his friends in the black community or holding Walsh’s campaign signs. He even had his mother, a retired school principal, record a robocall for Walsh.

“If there’s anything else I can do to help Marty Walsh get into office, I’ll do it,” he said.

To someone like Passacantilli, the fellowship found in recovery transcends all tribes. A grandson of the late Frederick C. Langone, a longtime city councilor, Passacantilli is president of the North End Waterfront Neighborhood Council. He quit his job working for the historically Italian neighborhood’s district City Councilor Salvatore LaMattina to work on Walsh’s campaign. That was well before LaMattina endorsed Walsh’s rival for mayor, Councilor at Large John R. Connolly.

“People look at me like, ‘Marty Walsh? He’s an Irish kid from Savin Hill and you’re an Italian kid from Hanover Street,’ ” said Passacantilli. “But we have that bond and no one else would understand it.”

“I’m Marty and Marty’s me,” Passacantilli added. “I identify with him and that’s how he helps me.”